The present invention is related to packaging of articles within flexible material containers preferably, but not necessarily, provided from a continuous web formed by two superimposed flat layers mutually joined to each other at least along one longitudinal edge thereof. Such webs considered suitable in connection with the packaging technique according to the invention may be constituted by a heat-weldable plastic material tubular film (and accordingly the two superimposed film layers shall evidently be mutually joined along both longitudinal edges thereof), or by a single-fold film also made of a heat-weldable plastic material (and in that case the two film layers shall evidently be mutually joined only along one longitudinal edge thereof). As it will be apparent in the following, the invention may be carried out not only in connection with plastic material films, but even as far as flexible material webs of different types are concerned, such as for instance coupled paper/plastic films, plastic film/plastic films, aluminium/plastic films, aluminium/polythenated paper and other multi-coupled webs. Moreover the invention can also be advantageously carried into effect in connection with packaging systems employing, instead of a continuous web, envelopes or the like flexible material containers having been previously pre-formed according to a substantially flat arrangement, with two edges designed to be mutually spread apart so as to allow introduction of the articles to be packaged therethrough.
From Italian Patent application IT-A-67207/96 an automatic machine for the packaging of articles starting from a plastic-material flat tubular film is known, which comprises a fill-in station to which the tubular film is fed to be then transversely cut so as to form a web length of a desired size. The apparatus further comprises means to spread apart the cut edges of the tubular film web length, grasp means to hold the edges during filling in of the articles, and means to sealingly close said edges following filling in. In this known apparatus the means to spread apart the cut edges of the web length comprise two nozzle assemblies to supply a flow of air under pressure substantially tangentially to the cut edges, so as to produce mutual spacing apart thereof under aerodynamic effect. The tubular film edges are thus moved towards respective abutment surfaces against which these edges are then engaged so as to be then further spaced apart from each other thereby bringing the film length into an open-bag configuration adapted to receive the articles to be packaged. At the end of the filling operation the edges are again brought near each other and sealingly closed by heat welding.
This known apparatus with the related air jet spreading system, while having proved sufficiently practical and functional, is affected by several limits and drawbacks.
The main limit is related to the type of material which can be employed for the packaging: this material, in order to ensure the necessary operative reliability of the pneumatic spreading apart system, can be neither too thin, nor too thick, since in both cases the correct mutual opening of the edges of the web lengths every time fed to the fill-in station might fail: actually a very thin material may give rise to fluttering of the edges under the air jets, while with a very thick material the air jets may produce no useful effect on the web length edges. Thus in practice the web which can be employed with the above reference known apparatus is as a rule consisting of a tubular polyethylene film having a thickness of about 0.6-0.13 mm. It would be instead desirable employing different and even more valuable materials, such as multi-coupled webs (paper/plastic films and the like), having not only a tubular configuration but also of the so called single-fold type, i.e. consisting of two layers superimposed to each other in a flat condition and mutually joined only along one longitudinal edge thereof.
A further drawback of the above referenced known apparatus resides in a relatively high risk of failed spreading apart of the edges of the web length each time supplied to the fill-in station, which involves the need of relatively frequent manual interventions.
Additional inconveniences of this known apparatus consist of the difficulty of properly adjusting the pneumatic spreading apart device, and also of a high energy consumption for generating the compressed air supplied to this spreading apart system.